Chapter 3: Solid Waste Disposal CHAPTER 3 SOLID WASTE DISPOSAL IPCC Guidelines for National Greenhouse Gas Inventories 3.1

Transcription

1 Chapter 3: Solid Waste Disposal CHAPTER 3 SOLID WASTE DISPOSAL 2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.1

2 Volume 5: Waste Authors Riitta Pipatti (Finland), Per Svardal (Norway) Joao Wagner Silva Alves (Brazil), Qingxian Gao (China), Carlos López Cabrera (Cuba), Katarina Mareckova (Slovakia), Hans Oonk (Netherlands), Elizabeth Scheehle (USA), Chhemendra Sharma (India), Alison Smith (UK), and Masato Yamada (Japan) Contributing Authors Jeffrey B. Coburn (USA), Kim Pingoud (Finland), Gunnar Thorsen (Norway), and Fabian Wagner (Germany) IPCC Guidelines for National Greenhouse Gas Inventories

3 Chapter 3: Solid Waste Disposal Contents 3 Solid Waste Disposal 3.1 Introduction Methodological issues Choice of method Choice of activity data Choice of emission factors and parameters Use of measurement in the estimation of CH 4 emissions from SWDS Carbon stored in SWDS Completeness Developing a consistent time series Uncertainty assessment Uncertainty attributable to the method Uncertainty attributable to data QA/QC, Reporting and Documentation References Annex 3A.1 First Order Decay Model References IPCC Guidelines for National Greenhouse Gas Inventories 3.3

4 Volume 5: Waste Equations Equation 3.1 CH 4 emission from SWDS Equation 3.2 Decomposable DOC from waste disposal data Equation 3.3 Transformation from DDOCm to L o Equation 3.4 DDOCm accumulated in the SWDS at the end of year T Equation 3.5 DDOCm decomposed at the end of year T Equation 3.6 CH 4 generated from decayed DDOCm Equation 3.7 Estimates DOC using default carbon content values Equation 3A1.1 Differential equation for first order decay Equation 3A1.2 First order decay equation Equation 3A1.3 DDOCm remaining after 1 year of decay Equation 3A1.4 DDOCm decomposed after 1 year of decay Equation 3A1.5 DDOCm decomposed in year T Equation 3A1.6 Relationship between half-life and reaction rate constant Equation 3A1.7 FOD equation for decay commencing after 3 months Equation 3A1.8 DDOCm decomposed in year of disposal (3 month delay) Equation 3A1.9 DDOCm dissimilated in year (t) (3 month delay) Equation 3A1.10 Mass of degradable organic carbon accumulated at the end of year T Equation 3A1.11 Mass of degradable organic carbon decomposed in year T Equation 3A1.12 DDOCm remaining at end of year of disposal Equation 3A1.13 DDOCm decomposed during year of disposal Equation 3A1.14 DDOCm accumulated at the end of year T Equation 3A1.15 DDOCm decomposed in year T Equation 3A1.16 Calculation of decomposable DOCm from waste disposal data Equation 3A1.17 CH 4 generated from decomposed DDOCm Equation 3A1.18 CH 4 emitted from SWDS Equation 3A1.19 Calculation of long-term stored DOCm from waste disposal data Equation 3A1.20 First order rate of reaction equation Equation 3A1.21 IPCC 1996 Guidelines equation for DOC reacting in year T Equation 3A1.22 IPCC 2000GPG FOD equation for DDOCm reacting in year T Equation 3A1.23 FOD with disposal rate D(t) Equation 3A1.24 Degradable organic carbon accumulated during a year Equation 3A1.25 CH 4 generated during a year IPCC Guidelines for National Greenhouse Gas Inventories

5 Chapter 3: Solid Waste Disposal Figures Figure 3.1 Decision Tree for CH 4 emissions from Solid Waste Disposal Sites Figure 3A1.1 Error introduced by not fully integrating the rate of reaction curve Figure 3A1.2 Effect of error in the GPG2000 equation Tables Table 3.1 SWDS classification and Methane Correction Factors (MCF) Table 3.2 Oxidation factor (OX) for SWDS Table 3.3 Recommended default methane generation rate (k) values under Tier Table 3.4 Recommended default Half-life (t 1/2 ) values (yr) under Tier Table 3.5 Estimates of uncertainties associated with the default activity data and parameters in the FOD method for CH 4 emissions from SWDS Table 3A1.1 New FOD calculating method Boxes Box 3.1 Direct measurements from gas collection systems to estimate FOD model parameters Box 3.2 Direct measurements of methane emissions from the SWDS surface IPCC Guidelines for National Greenhouse Gas Inventories 3.5

6 Volume 5: Waste 3 SOLID WASTE DISPOSAL 3.1 INTRODUCTION Treatment and disposal of municipal, industrial and other solid waste produces significant amounts of methane (CH 4 ). In addition to CH 4, solid waste disposal sites (SWDS) also produce biogenic carbon dioxide (CO 2 ) and non-methane volatile organic compounds (NMVOCs) as well as smaller amounts of nitrous oxide (N 2 O), nitrogen oxides (NO x ) and carbon monoxide (CO). CH 4 produced at SWDS contributes approximately 3 to 4 percent to the annual global anthropogenic greenhouse gas emissions (IPCC, 2001). In many industrialised countries, waste management has changed much over the last decade. Waste minimisation and recycling/reuse policies have been introduced to reduce the amount of waste generated, and increasingly, alternative waste management practices to solid waste disposal on land have been implemented to reduce the environmental impacts of waste management. Also, landfill gas recovery has become more common as a measure to reduce CH 4 emissions from SWDS. Decomposition of organic material derived from biomass sources (e.g., crops, wood) is the primary source of CO 2 released from waste. These CO 2 emissions are not included in national totals, because the carbon is of biogenic origin and net emissions are accounted for under the AFOLU Sector. Methodologies for NMVOCs, NO x and CO are covered in guidelines under other conventions such as the UNECE Convention on Long Range Transboundary Air Pollution (CLRTAP). Links to these methodologies are provided in Chapter 1 of this volume, and additional information in Chapter 7 of Volume 1. No methodology is provided for N 2 O emissions from SWDS because they are not significant. The Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (1996 Guidelines, IPCC, 1997) and the Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories (GPG2000, IPCC, 2000) described two methods for estimating CH 4 emissions from SWDS: the mass balance method (Tier 1) and the First Order Decay (FOD) method (Tier 2). In this Volume, the use of the mass balance method is strongly discouraged as it produces results that are not comparable with the FOD method which produces more accurate estimates of annual emissions. In place of the mass balance method, this chapter provides a Tier 1 version of the FOD method including a simple spreadsheet model with step-by-step guidance and improved default data. With this guidance, all countries should be able to implement the FOD method. 3.2 METHODOLOGICAL ISSUES Choice of method The IPCC methodology for estimating CH 4 emissions from SWDS is based on the First Order Decay (FOD) method. This method assumes that the degradable organic component (degradable organic carbon, DOC) in waste decays slowly throughout a few decades, during which CH 4 and CO 2 are formed. If conditions are constant, the rate of CH 4 production depends solely on the amount of carbon remaining in the waste. As a result emissions of CH 4 from waste deposited in a disposal site are highest in the first few years after deposition, then gradually decline as the degradable carbon in the waste is consumed by the bacteria responsible for the decay. Transformation of degradable material in the SWDS to CH 4 and CO 2 is by a chain of reactions and parallel reactions. A full model is likely to be very complex and vary with the conditions in the SWDS. However, laboratory and field observations on CH 4 generation data suggest that the overall decomposition process can be approximated by first order kinetics (e.g., Hoeks, 1983), and this has been widely accepted. IPCC has therefore adopted the relatively simple FOD model as basis for the estimation of CH 4 emissions from SWDS. Half-lives for different types of waste vary from a few years to several decades or longer. The FOD method requires data to be collected or estimated for historical disposals of waste over a time period of 3 to 5 half-lives in order to achieve an acceptably accurate result. It is therefore good practice to use disposal data for at least 50 years as this time frame provides an acceptably accurate result for most typical disposal practices and conditions. If a shorter time frame is chosen, the inventory compiler should demonstrate that there will be no significant underestimation of the emissions. These Guidelines provide guidance on how to estimate historical waste disposal data (Section 3.2.2, Choice of Activity Data), default values for all the parameters of the FOD model IPCC Guidelines for National Greenhouse Gas Inventories

7 Chapter 3: Solid Waste Disposal (Section 3.2.3, Choice of Emission Factors and Parameters), and a simple spreadsheet model to assist countries in using the FOD method. Three tiers to estimate the CH 4 emissions from SWDS are described: Tier 1: The estimations of the Tier 1 methods are based on the IPCC FOD method using mainly default activity data and default parameters. Tier 2: Tier 2 methods use the IPCC FOD method and some default parameters, but require good quality country-specific activity data on current and historical waste disposal at SWDS. Historical waste disposal data for 10 years or more should be based on country-specific statistics, surveys or other similar sources. Data are needed on amounts disposed at the SWDS. Tier 3: Tier 3 methods are based on the use of good quality country-specific activity data (see Tier 2) and the use of either the FOD method with (1) nationally developed key parameters, or (2) measurement derived country-specific parameters. The inventory compiler may use country-specific methods that are of equal or higher quality to the above defined FOD-based Tier 3 method. Key parameters should include the half-life, and either methane generation potential (L o ) or DOC content in waste and the fraction of DOC which decomposes (DOC f ). These parameters can be based on measurements as described in Box 3.1. A decision tree for choosing the most appropriate method appears in Figure 3.1. It is good practice for all countries to use the FOD method or a validated country-specific method, in order to account for time dependence of the emissions. The FOD method is briefly described in Section and in more detail in Annex 3A.1. A spreadsheet model has been developed by the IPCC to assist countries in implementing the FOD: IPCC Spreadsheet for Estimating Methane Emissions from Solid Waste Disposal Sites (IPCC Waste Model) 1.The IPCC Waste Model is described in more detail below and can be modified and used for all tiers. Figure 3.1 Decision Tree for CH 4 emissions from Solid Waste Disposal Sites Start Are good quality country-specific activity data on historical and current waste disposal 1 available? Yes Are country-specific models or key parameters 2 available? Yes Estimate emissions using country-specific methods or IPCC FOD method with country-specific key parameters and good quality country-specific activity data. No Is solid waste disposal on land a key category 3? Collect current waste disposal data and estimate historical data using guidance in Section Yes No No Box 3: Tier 3 Estimate emissions using the IPCC FOD method with default parameters and good quality country-specific activity data. Box 2: Tier 2 Estimate Emissions using the IPCC FOD method with default data to fill in missing country-specific data. Box 1: Tier 1 Note: 1. Good quality country-specific activity data mean country-specific data on waste disposed in SWDS for 10 years or more. 2. Key parameters mean DOC/L o, DOC f and half-life time. 3. See Volume 1 Chapter 4, "Methodological Choice and Identification of Key Categories" (noting Section on limited resources), for discussion of key categories and use of decision trees. 1 See the attached spreadsheets in Excel format. <IPCC_Waste_Model.xls> IPCC Guidelines for National Greenhouse Gas Inventories 3.7

8 Volume 5: Waste FIRST ORDER DECAY (FOD) METHANE EMISSIONS The CH 4 emissions from solid waste disposal for a single year can be estimated using Equations 3.1. CH 4 is generated as a result of degradation of organic material under anaerobic conditions. Part of the CH 4 generated is oxidised in the cover of the SWDS, or can be recovered for energy or flaring. The CH 4 actually emitted from the SWDS will hence be smaller than the amount generated. EQUATION 3.1 CH 4 EMISSION FROM SWDS CH4 Emissions = CH 4 generatedx T RT ( 1 OX x, T Where: CH 4 Emissions = CH 4 emitted in year T, Gg T = inventory year x = waste category or type/material R T = recovered CH 4 in year T, Gg OX T = oxidation factor in year T, (fraction) The CH 4 recovered must be subtracted from the amount CH 4 generated. Only the fraction of CH 4 that is not recovered will be subject to oxidation in the SWDS cover layer. ) METHANE GENERATION The CH 4 generation potential of the waste that is disposed in a certain year will decrease gradually throughout the following decades. In this process, the release of CH 4 from this specific amount of waste decreases gradually. The FOD model is built on an exponential factor that describes the fraction of degradable material which each year is degraded into CH 4 and CO 2. One key input in the model is the amount of degradable organic matter (DOCm) in waste disposed into SWDS. This is estimated based on information on disposal of different waste categories (municipal solid waste (MSW), sludge, industrial and other waste) and the different waste types/material (food, paper, wood, textiles, etc.) included in these categories, or alternatively as mean DOC in bulk waste disposed. Information is also needed on the types of SWDS in the country and the parameters described in Section For Tier 1, default regional activity data and default IPCC parameters can be used and these are included in the spreadsheet model. Tiers 2 and 3 require country-specific activity data and/or country-specific parameters. The equations for estimating the CH 4 generation are given below. As the mathematics are the same for estimating the CH 4 emissions from all waste categories/waste types/materials, no indexing referring to the different categories/waste materials/types is used in the equations below. The CH 4 potential that is generated throughout the years can be estimated on the basis of the amounts and composition of the waste disposed into SWDS and the waste management practices at the disposal sites. The basis for the calculation is the amount of Decomposable Degradable Organic Carbon (DDOCm) as defined in Equation 3.2. DDOCm is the part of the organic carbon that will degrade under the anaerobic conditions in SWDS. It is used in the equations and spreadsheet models as DDOCm. The index m is used for mass. DDOCm equals the product of the waste amount (W), the fraction of degradable organic carbon in the waste (DOC), the fraction of the degradable organic carbon that decomposes under anaerobic conditions (DOC f ), and the part of the waste that will decompose under aerobic conditions (prior to the conditions becoming anaerobic) in the SWDS, which is interpreted with the methane correction factor (MCF) IPCC Guidelines for National Greenhouse Gas Inventories

9 Chapter 3: Solid Waste Disposal Where: DDOCm = EQUATION 3.2 DECOMPOSABLE DOC FROM WASTE DISPOSAL DATA DDOCm = W DOC DOC mass of decomposable DOC deposited, Gg f MCF W = mass of waste deposited, Gg DOC = degradable organic carbon in the year of deposition, fraction, Gg C/Gg waste DOC f = fraction of DOC that can decompose (fraction) MCF = CH 4 correction factor for aerobic decomposition in the year of deposition (fraction) Although CH 4 generation potential (L o ) 2 is not used explicitly in these Guidelines, it equals the product of DDOCm, the CH 4 concentration in the gas (F) and the molecular weight ratio of CH 4 and C (16/12). EQUATION 3.3 TRANSFORMATION FROM DDOCm TO L O L o = DDOCm F 16 /12 Where: L o = CH 4 generation potential, Gg CH 4 DDOCm = mass of decomposable DOC, Gg F = fraction of CH 4 in generated landfill gas (volume fraction) 16/12 = molecular weight ratio CH 4 /C (ratio) Using DDOCma (DDOCm accumulated in the SWDS) from the spreadsheets, the above equation can be used to calculate the total CH 4 generation potential of the waste remaining in the SWDS. FIRST ORDER DECAY BASICS With a first order reaction, the amount of product is always proportional to the amount of reactive material. This means that the year in which the waste material was deposited in the SWDS is irrelevant to the amount of CH 4 generated each year. It is only the total mass of decomposing material currently in the site that matters. This also means that when we know the amount of decomposing material in the SWDS at the start of the year, every year can be regarded as year number 1 in the estimation method, and the basic first order calculations can be done by these two simple equations, with the decay reaction beginning on the 1 st of January the year after deposition. EQUATION 3.4 DDOCm ACCUMULATED IN THE SWDS AT THE END OF YEAR T DDOCma k ( DDOCma e ) T = DDOCmdT + T 1 EQUATION 3.5 DDOCm DECOMPOSED AT THE END OF YEAR T DDOCm decomp T = DDOCma 1 T 1 k ( e ) 2 In the 2006 Guidelines L o (Gg CH 4 generated) is estimated from the amount of decomposable DOC in the SWDS. The equation in GPG2000 is different as L o is estimated as Gg CH 4 per Gg waste disposed, and the emissions are obtained by multiplying with the mass disposed IPCC Guidelines for National Greenhouse Gas Inventories 3.9

10 Volume 5: Waste Where: T = inventory year DDOCma T = DDOCm accumulated in the SWDS at the end of year T, Gg DDOCma T-1 = DDOCm accumulated in the SWDS at the end of year (T-1), Gg DDOCmd T = DDOCm deposited into the SWDS in year T, Gg DDOCm decomp T = DDOCm decomposed in the SWDS in year T, Gg k = reaction constant, k = ln(2)/t 1/2 (y -1 ) t 1/2 = half-life time (y) The method can be adjusted for reaction start dates earlier than 1 st of January in the year after deposition. Equations and explanations can be found in Annex 3A.1. CH 4 generated from decomposable DDOCm The amount of CH 4 formed from decomposable material is found by multiplying the CH 4 fraction in generated landfill gas and the CH 4 /C molecular weight ratio. EQUATION 3.6 CH 4 GENERATED FROM DECAYED DDOCm CH generated = DDOCm decomp F 16 /12 4 T Where: CH 4 generated T = amount of CH 4 generated from decomposable material DDOCm decomp T = DDOCm decomposed in year T, Gg F = fraction of CH 4, by volume, in generated landfill gas (fraction) 16/12 = molecular weight ratio CH 4 /C (ratio) T Further background details on the FOD, and an explanation of differences with the approaches in previous versions of the guidance (IPCC, 1997; IPCC, 2000), are given in Annex 3A.1. SIMPLE FOD SPREADSHEET MODEL The simple FOD spreadsheet model (IPCC Waste Model) has been developed on the basis of Equations 3.4 and 3.5 shown above. The spreadsheet keeps a running total of the amount of decomposable DOC in the disposal site, taking account of the amount deposited each year and the amount remaining from previous years. This is used to calculate the amount of DOC decomposing to CH 4 and CO 2 each year. The spreadsheet also allows users to define a time delay between deposition of the waste and the start of CH 4 generation. This represents the time taken for substantial CH 4 to be generated from the disposed waste (see Section and Annex 3A.1). The model then calculates the amount of CH 4 generated from the DDOCm, and subtracts the CH 4 recovered and CH 4 oxidised in the cover material (see Annex 3A.1 for equations) to give the amount of CH 4 emitted. The IPCC Waste Model provides two options for the estimation of the emissions from MSW, that can be chosen depending on the available activity data. The first option is a multi-phase model based on waste composition data. The amounts of each type of degradable waste material (food, garden and park waste 3, paper and cardboard, wood, textiles, etc.) in MSW are entered separately. The second option is single-phase model based on bulk waste (MSW). Emissions from industrial waste and sludge are estimated in a similar way as for bulk MSW. Countries that choose to use the spreadsheet model may use either the waste composition or the bulk waste option, depending on the level of data available. When waste composition is relatively stable, both options give similar results. However when rapid changes in waste composition occur, options might give different 3 garden waste may also be called yard waste in US English IPCC Guidelines for National Greenhouse Gas Inventories

11 Chapter 3: Solid Waste Disposal outputs. For example, changes in waste management, such as bans to dispose food waste or degradable organic materials, can result in rapid changes in the composition of waste disposed in SWDS. Both options can be used for estimating the carbon in harvested wood products (HWP) that is long-term stored in SWDS (see Volume 4, Chapter 12, Harvested Wood Products). If no national data are available on bulk waste, it is good practice to use the waste composition option in the spreadsheets, using the provided IPCC default data for waste composition. In the spreadsheet model, separate values for DOC and the decay half-life may be entered for each waste category and in the waste composition option also for each waste type/material. The decay half-life can also be assumed to be the same for all waste categories and/or waste types. The first approach assumes that decomposition of different waste types/materials in a SWDS is completely independent of each other; the second approach assumes that decomposition of all types of waste is completely dependent on each other. At the time of writing these Guidelines, no evidence exists that one approach is better than the other (see Section 3.2.3, Halflife). The spreadsheet calculates the amount of CH 4 generated from each waste component on a different worksheet. The methane correction factor (MCF see Section 3.2.3) is entered as a weighted average for all disposal sites in the country. MCF may vary by time to take account of changes in waste management practices (such as a move towards more managed SWDS or deeper sites). Finally, the amount of CH 4 generated from each waste category and type/material is summed, and the amounts of CH 4 recovered and oxidised in the cover material are subtracted (if applicable), to give an estimate of total CH 4 emissions. For the bulk waste option, DOC can be a weighted average for MSW. The spreadsheet model is most useful to Tier 1 methods, but can be adapted for use with all tiers. For Tier 1 the spreadsheets can estimate the activity data from population data and disposal data per capita (for MSW) and GDP (industrial waste), see Section for additional guidance. When Tier 2 and 3 approaches are used, countries can extend the spreadsheet model to meet their own demands, or create their own models. The spreadsheet model can be extended with more sheets to calculate the CH 4 emissions if needed. MCF, OX and DOC for bulk waste can be made to vary over time. The same can easily be done to other parameters like DOC f. New half-lives will require new CH 4 calculating sheets. Countries with good data on industrial waste can add new CH 4 calculating sheets and calculate the CH 4 emissions separately for different types of industrial waste. When the spreadsheet model is modified or countries-specific models are used, key assumptions and parameters should be transparently documented. Details on how to use the spreadsheet model can be found in the Instructions spreadsheet. The model can be copied from the 2006 Guidelines CDROM or downloaded from the IPCC NGGIP website < >. Modelling different geographical or climate regions It is possible to estimate CH 4 generation in different geographical regions of the country. For example, if the country contains a hot and wet region and a hot and dry region, the decay rates will be different in each region. Dealing with different waste categories Some users may find that their national waste statistics do not match the categories used in the model (food, garden and park waste, paper and cardboard, textiles and others as well as industrial waste). Where this is the case, the spreadsheet model will need to be modified to correspond to categorisation used by the country, or country-specific waste types will need to be re-classified into the IPCC categories. For example, clothes, curtain, and rugs are included in textiles, kitchen waste is similar to food waste, and straw and bamboo are similar to wood. The national statistics may contain a category called street sweepings. The user should estimate the composition of this waste. For example, it may be 50 percent inert material, 10 percent food, 30 percent paper and 10 percent garden and park waste. The street sweepings category can then be divided into these IPCC categories and added on to the waste already in these categories. In a similar manner, furniture can be divided into wood, plastic or metal waste, and electronics to metal, plastic and glass waste. This can all be done in a separate worksheet set up by the inventory compiler. Adjusting waste composition at generation to waste composition at SWDS The user should establish whether national waste composition statistics refer to the composition of waste generated or waste received at SWDS. The default waste composition statistics presented here are the composition of waste generated, not waste sent to SWDS. The composition should therefore be adjusted if necessary to take account of the impact of recycling or composting activities on the composition of the waste sent to SWDS. This could be best done in a separate spreadsheet set up by the inventory compiler, to estimate 2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.11

12 Volume 5: Waste the amounts of each waste material generated, then subtract estimates of the amount of each waste material recycled, incinerated or composted, and work out the new composition of the residual waste sent to SWDS. Open burning of waste at SWDS Open burning at SWDS is common in many developing countries. The amount of waste (and DDOCm) available for decay at SWDS should be adjusted to the amount burned. Chapter 5 provides methods how to estimate the amount of waste burned. The estimation of emissions from SWDS should be consistent with estimates for open burning of waste at the disposal sites Choice of activity data Activity data consist of the waste generation for bulk waste or by waste component and the fraction of waste disposed to SWDS. Waste generation is the product of the per capita waste generation rate (tonnes/capita/yr) for each component and population (capita). Chapter 2 gives guidance on the collection of data on waste generation and waste composition as well as waste management practices. Regional default values for MSW can be found in Table 2.1 for the generation rate and the fraction disposed in SWDS, and Table 2.3 for the waste composition. For industrial waste default data can be found in Table 2.2. To achieve accurate emission estimates in national inventories it is usually necessary to include data on solid waste disposal (amount, composition) for 3 to 5 half-lives (see Section 3.2.3) of the waste deposited at the SWDS, and specifications of different half-lives for different components of the waste stream or for bulk waste by SWDS type (IPCC, 2000). Changes in waste management practices (e.g., site covering/capping, leachate drainage improvement, compacting, and prohibition of hazardous waste disposal together with MSW) should also be taken into account when compiling historical data. The FOD methods require data on solid waste disposal (amounts and composition) that are collected by default for 50 years. Countries that do not have historical statistical data, or equivalent data on solid waste disposal that go back for the whole period of 50 years or more will need to estimate these data using surrogates (extrapolation with population, economic or other drivers). The choice of the method will depend on the availability of data in the country. For countries using default data on MSW disposal on land, or for countries whose own data do not cover the past 50 years, the missing historical data can be estimated to be proportional to urban population 4 (or total population when historical data on urban population are not available, or in cases where waste collection covers the whole population). For countries having national data on MSW generation, management practices and composition over a period of years (Tier 2 FOD), analyses on the drivers for solid waste disposal are encouraged. The historical data could be proportional to economic indicators, or combinations of population and economic indicators. Trend extrapolation could also produce good results. Waste management policies to reduce waste generation and to promote alternatives to solid waste disposal should be taken into account in the analyses. Data on industrial production (amount or value of production, preferably by industry type, depending on availability of data) are recommended as surrogate for the estimation of disposal of industrial waste (Tier 2). When production data are not available, historical disposal of industrial waste can be estimated proportional to GDP or other economic indicators. GDP is used as the driver in the Tier 1 method. Historical data on urban population (or total population), GDP (or other economic indicators) and statistics in industrial production can be obtained from national statistics. International databases can help when national data are not available, for example: Population data (1950 onwards with five-year intervals) can be found in UN Statistics (see GDP data (1970 onwards, annual data at current prices in national currency) can be found in UN Statistics (see For those years data are not available interpolation or extrapolation can be used. Alternative methods have been put forward in literature and can be used when they can be shown to give better estimates than the above-mentioned default methods. The choice of method and surrogate, and the reasoning behind the choice, should be documented transparently in the inventory report. The use of surrogate methods, interpolation and extrapolation as means to derive missing data is described in more detail in Chapter 6, Time Series Consistency, in Volume 1. 4 The choice between urban population and total population should be guided by the coverage of waste collection. When data on coverage of waste collection is not available, the recommendation is to use urban population as the driver IPCC Guidelines for National Greenhouse Gas Inventories

13 Chapter 3: Solid Waste Disposal Choice of emission factors and parameters DEGRADABLE ORGANIC CARBON (DOC) Degradable organic carbon (DOC) is the organic carbon in waste that is accessible to biochemical decomposition, and should be expressed as Gg C per Gg waste. The DOC in bulk waste is estimated based on the composition of waste and can be calculated from a weighted average of the degradable carbon content of various components (waste types/material) of the waste stream. The following equation estimates DOC using default carbon content values: EQUATION 3.7 ESTIMATES DOC USING DEFAULT CARBON CONTENT VALUES DOC = ( DOC i W i ) Where: DOC = fraction of degradable organic carbon in bulk waste, Gg C/Gg waste DOC i = fraction of degradable organic carbon in waste type i e.g., the default value for paper is 0.4 (wet weight basis) W i = fraction of waste type i by waste category e.g., the default value for paper in MSW in Eastern Asia is (wet weight basis) i The default DOC values for these fractions for MSW can be found in Table 2.4 and for industrial waste by industry in Table 2.5 in Chapter 2 of this Volume. A similar approach can be used to estimate the DOC content in total waste disposed in the country. In the spreadsheet model, the estimation of the DOC in MSW is needed only for the bulk waste option, and is the average DOC for the MSW disposed in the SWDS, including inert materials. The inert part of the waste (glass, plastics, metals and other non-degradable waste, see defaults in Table 2.3 in Chapter 2.) is important when estimating the total amount of DOC in MSW. Therefore it is advised not to use IPCC default waste composition data together with country-specific MSW disposal data, without checking that the inert part is close to the inert part in the IPCC default data. The use of country-specific values is encouraged if data are available. Country-specific values can be obtained by performing waste generation studies, sampling at SWDS combined with analysis of the degradable carbon content within the country. If national values are used, survey data and sampling results should be reported (see also Section for activity data and Section 3.8 for reporting). FRACTION OF DEGRADABLE ORGANIC CARBON WHICH DECOMPOSES (DOC f ) Fraction of degradable organic carbon which decomposes (DOC f ) is an estimate of the fraction of carbon that is ultimately degraded and released from SWDS, and reflects the fact that some degradable organic carbon does not degrade, or degrades very slowly, under anaerobic conditions in the SWDS. The recommended default value for DOC f is 0.5 (under the assumption that the SWDS environment is anaerobic and the DOC values include lignin, see Table 2.4 in Chapter 2 for default DOC values) (Oonk and Boom, 1995; Bogner and Matthews, 2003). DOC f value is dependent on many factors like temperature, moisture, ph, composition of waste, etc. National values for DOC f or values from similar countries can be used for DOC f, but they should be based on well-documented research. The amount of DOC leached from the SWDS is not considered in the estimation of DOC f. Generally the amounts of DOC lost with the leachate are less than 1 percent and can be neglected in the calculations 5. Higher tier methodologies (Tier 2 or 3) can also use separate DOC f values defined for specific waste types. There is some literature giving information about anaerobic degradability (DOC f ) for material types (Barlaz, 5 In countries with high precipitation rates the amount of DOC lost through leaching may be higher. In Japan, where the precipitation is high, SWDS with high penetration rate, have been found to leach significant amounts of DOC (sometimes more than 10 percent of the carbon in the SWDS) (Matsufuji et al., 1996) IPCC Guidelines for National Greenhouse Gas Inventories 3.13

14 Volume 5: Waste 2004; Micales & Skog, 1997; US EPA, 2002; Gardner et al., 2002). The reported degradabilities especially for wood, vary over a wide range and is yet quite inconclusive. They may also vary with tree species. Separate DOC f values for specific waste types imply the assumption that degradation of different types of waste is independent of each other. As discussed further, below under Half-Life, scientific knowledge at the moment of writing these Guidelines is not yet conclusive on this aspect. Hence the use of waste type specific values for DOC f can introduce additional uncertainty to the estimates in cases where the data on waste composition are based on default values, modelling or estimates based on expert judgement. Therefore, it is good practice to use DOC f values specific to waste types only when waste composition data are based on representative sampling and analyses. METHANE CORRECTION FACTOR (MCF) 6 Waste disposal practices vary in the control, placement of waste and management of the site. The CH 4 correction factor (MCF) accounts for the fact that unmanaged SWDS produce less CH 4 from a given amount of waste than anaerobic managed SWDS. In unmanaged SWDS, a larger fraction of waste decomposes aerobically in the top layer. In unmanaged SWDS with deep disposal and/or with high water table, the fraction of waste that degrades aerobically should be smaller than in shallow SWDS. Semi-aerobic managed SWDS are managed passively to introduce air to the waste layer to create a semi-aerobic environment within the SWDS. The MCF in relation to solid waste management is specific to that area and should be interpreted as the waste management correction factor that reflects the management aspect it encompasses. An MCF is assigned to each of four categories, as shown in Table 3.1. A default value is provided for countries where the quantity of waste disposed to each SWDS is not known. A country s classification of its waste sites into managed or unmanaged may change over a number of years as national waste management policies are implemented. The Fraction of Solid Waste Disposed to Solid Waste Disposal Sites (SW F ) and MCF reflect the way waste is managed and the effect of site structure and management practices on CH 4 generation. The methodology requires countries to provide data or estimates of the quantity of waste that is disposed of to each of four categories of solid waste disposal sites (Table 3.1). Only if countries cannot categorise their SWDS into four categories of managed and unmanaged SWDS, the MCF for uncategorised SWDS can be used. Type of Site TABLE 3.1 SWDS CLASSIFICATION AND METHANE CORRECTION FACTORS (MCF) Methane Correction Factor (MCF) Default Values Managed anaerobic Managed semi-aerobic Unmanaged 3 deep ( >5 m waste) and /or high water table 0.8 Unmanaged 4 shallow (<5 m waste) 0.4 Uncategorised SWDS Anaerobic managed solid waste disposal sites: These must have controlled placement of waste (i.e., waste directed to specific deposition areas, a degree of control of scavenging and a degree of control of fires) and will include at least one of the following: (i) cover material; (ii) mechanical compacting; or (iii) levelling of the waste. 2 Semi-aerobic managed solid waste disposal sites: These must have controlled placement of waste and will include all of the following structures for introducing air to waste layer: (i) permeable cover material; (ii) leachate drainage system; (iii) regulating pondage; and (iv) gas ventilation system. 3 Unmanaged solid waste disposal sites deep and/or with high water table: All SWDS not meeting the criteria of managed SWDS and which have depths of greater than or equal to 5 metres and/or high water table at near ground level. Latter situation corresponds to filling inland water, such as pond, river or wetland, by waste. 4 Unmanaged shallow solid waste disposal sites; All SWDS not meeting the criteria of managed SWDS and which have depths of less than 5 metres. 5 Uncategorised solid waste disposal sites: Only if countries cannot categorise their SWDS into above four categories of managed and unmanaged SWDS, the MCF for this category can be used. Sources: IPCC (2000); Matsufuji et al. (1996) 6 The term methane correction factor (MCF) in this context should not be confused with the methane conversion factor (MCF) referred to in the Agriculture, Forestry, and Other Land Use Sector for livestock manure management emissions IPCC Guidelines for National Greenhouse Gas Inventories

15 Chapter 3: Solid Waste Disposal FRACTION OF CH 4 IN GENERATED LANDFILL GAS (F) Most waste in SWDS generates a gas with approximately 50 percent CH 4. Only material including substantial amounts of fat or oil can generate gas with substantially more than 50 percent CH 4. The use of the IPCC default value for the fraction of CH 4 in landfill gas (0.5) is therefore encouraged. The fraction of CH 4 in generated landfill gas should not be confused with measured CH 4 in gas emitted from the SWDS. In the SWDS, CO 2 is absorbed in seepage water, and the neutral condition of the SWDS transforms much of the absorbed CO 2 to bicarbonate. Therefore, it is good practice to adjust for the CO 2 absorption in seepage water, if the fraction of CH 4 in landfill gas is based on measurements of CH 4 concentrations measured in landfill gas emitted from the SWDS (Bergman, 1995; Kämpfer and Weissenfels, 2001; IPCC, 1997). OXIDATION FACTOR (OX) The oxidation factor (OX) reflects the amount of CH 4 from SWDS that is oxidised in the soil or other material covering the waste. CH 4 oxidation is by methanotrophic micro-organisms in cover soils and can range from negligible to 100 percent of internally produced CH 4. The thickness, physical properties and moisture content of cover soils directly affect CH 4 oxidation (Bogner and Matthews, 2003). Studies show that sanitary, well-managed SWDS tend to have higher oxidation rates than unmanaged dump sites. The oxidation factor at sites covered with thick and well-aerated material may differ significantly from sites with no cover or where large amounts of CH 4 can escape through cracks/fissures in the cover. Field and laboratory CH 4 and CO 2 emission concentrations and flux measurements that determine CH 4 oxidation from uniform and homogeneous soil layers should not be used directly to determine the oxidation factor, since in reality, only a fraction of the CH 4 generated will diffuse through such a homogeneous layer. Another fraction will escape through cracks/fissures or via lateral diffusion without being oxidised. Therefore, unless the spatial extent of measurements is wide enough and cracks/fissures are explicitly included, results from field and laboratory studies may lead to over-estimation of oxidation in SWDS cover soils. The default value for oxidation factor is zero. See Table 3.2. The use of the oxidation value of 0.1 is justified for covered, well-managed SWDS to estimate both diffusion through the cap and escape by cracks/fissures. The use of an oxidation value higher than 0.1, should be clearly documented, referenced, and supported by data relevant to national circumstances. It is important to remember that any CH 4 that is recovered must be subtracted from the amount generated before applying an oxidation factor. Type of Site TABLE 3.2 OXIDATION FACTOR (OX) FOR SWDS Oxidation Factor (OX) Default Values Managed 1, unmanaged and uncategorised SWDS 0 Managed covered with CH 4 oxidising material Managed but not covered with aerated material 2 Examples: soil, compost HALF-LIFE The half-life value, t 1/2 is the time taken for the DOCm in waste to decay to half its initial mass. In the FOD model and in the equations in this Volume, the reaction constant k is used. The relationship between k and t 1/2 is: k = ln(2)/t 1/2. The half-life is affected by a wide variety of factors related with the composition of the waste, climatic conditions at the site where the SWDS is located, characteristics of the SWDS, waste disposal practices and others (Pelt et al., 1998; Environment Canada, 2003). The half-life value applicable to any single SWDS is determined by a large number of factors associated with the composition of the waste and the conditions at the site. Recent studies have provided more data on half-lives 2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.15

16 Volume 5: Waste (experimental or by means of models), but the results obtained are based on the characteristics of developed countries under temperate conditions. Few available results reflect the characteristics of developing countries and tropical conditions. Measurements from SWDS in Argentina, New Zealand, the United States, the United Kingdom and the Netherlands support values for t 1/2 in the range of approximately 3 to 35 years (Oonk and Boom, 1995; USEPA, 2005; Scharff et al., 2003; Canada, 2004; and Argentina, 2004). The most rapid rates (k = 0.2, or a half-life of about 3 years) are associated with high moisture conditions and rapidly degradable material such as food waste. The slower decay rates (k = 0.02, or a half-life of about 35 years) are associated with dry site conditions and slowly degradable waste such as wood or paper. A much longer halflife of 70 years or above could be justified for shallow dry SWDS in a temperate climate or for wood waste in a dry, temperate climate. A half-life of less than 3 years may be appropriate for managed SWDS in a wet, temperate climate or rapidly degrading waste in a wet, tropical climate. The inventory compiler is encouraged to establish country specific half-life values. Current knowledge and data limitations constrain the development of a default methodology for estimating half-lives from field-data at SWDS. There are two alternative approaches to select the half-life (or k value) for the calculation: (a) calculate a weighted average for t 1/2 for mixed MSW (Jensen and Pipatti, 2002) or (b) divide the waste stream into categories of waste according to their degradation speed (Brown et al., 1999). The first approach assumes degradation of different types of waste to be completely dependent on each other. So the decay of wood is enhanced due to the present of food waste, and the decay of food waste is slowed down due to the wood. The second approach assumes degradation of different types of waste is independent of each other. Wood degrades as wood, irrespective whether it is in an almost inert SWDS or in a SWDS that contains large amounts of more rapidly degrading wastes. In reality the truth will probably be somewhere in the middle. However there has been little research performed to identify the better one of both approaches (Oonk and Boom, 1995; Scharff et al., 2003) and this research was not conclusive. Two options of the IPCC spreadsheet model apply either of above approaches to select the half-life as follows: Bulk waste option: The bulk waste option requires alternative (a) above, and is suitable for countries without data or with limited data on waste composition, but with good information on bulk waste disposed at SWDS. Default values are estimated as a function of the climate zone. Waste composition option: The waste composition option requires alternative (b) and is applicable for countries having data on waste composition. Specification of the half-life (t 1/2 ) of each component of the waste stream (IPCC, 2000) is required to achieve acceptably accurate results. For both options default half-life values are estimated as a function of the climate zone. The main assumptions and considerations made are: Waste composition (especially the organic component) is one of the main factors influencing both the amount and the timing of CH 4 production. Moisture content of a SWDS is an essential element for anaerobic decomposition and CH 4 generation. A simplified method assumes that the moisture content of a SWDS is proportional to the mean annual precipitation (MAP) in the location of the SWDS (Pelt et al., 1998; U.S. EPA, 1998; Environment Canada, 2003) or to the ratio of MAP and potential evapotranspiration (PET). The extent to which ambient air temperatures influence the temperature of the SWDS and gas generation rates depends mainly on the degree of waste management and the depth of SWDS. Wastes in shallow open dumps generally decompose aerobically and produce little CH 4, and the emissions decline in shorter time than the anaerobic conditions. Managed (and also deep unmanaged) SWDS creates anaerobic conditions. Countries may develop specific half-life values (or k values) more appropriate for their circumstances and characteristics. It is good practice that countries which develop their own half-life values document the experimental procedures used to derive to them IPCC Guidelines for National Greenhouse Gas Inventories

17 Chapter 3: Solid Waste Disposal Default k values and the corresponding half-lives are provided below in Table 3.3 and in Table 3.4. TABLE 3.3 RECOMMENDED DEFAULT METHANE GENERATION RATE (k ) VALUES UNDER TIER 1 (Derived from k values obtained in experimental measurements, calculated by models, or used in greenhouse gas inventories and other studies) Slowly degrading waste Moderately degrading waste Rapidly degrading waste Type of Waste Paper/textiles waste Wood/ straw waste Other (non food) organic putrescible/ Garden and park waste Food waste/sewage sludge Boreal and Temperate (MAT 20 C) Dry (MAP/PET < 1) Wet (MAP/PET > 1) Climate Zone* Dry (MAP < 1000 mm) Tropical 1 (MAT > 20 C) Moist and Wet (MAP 1000 mm) Default Range 2 Default Range 2 Default Range 2 Default Range , , , , , , Bulk Waste The available information on the determination of k and half-lives in tropical conditions is quite limited. The values included in the table, for those conditions, are indicative and mostly have been derived from the assumptions described in the text and values obtained for temperate conditions. 2 The range refers to the minimum and maximum data reported in literature or estimated by the authors of the chapter. It is included, basically, to describe the uncertainty associated with the default value. 3 Oonk and Boom (1995). 4 IPCC (2000). 5 Brown et al. (1999). A near value (16 yr) was used, for slow degradability, in the GasSim model verification (Attenborough et al., 2002). 6 Environment Canada (2003). 7 In this range are reported longer half-lives values (up to 231 years) that were not included in the table since are derived from extremely low k values used in sites with mean daily temperature < 0ºC (Levelton, 1991). 8 Estimated from RIVM (2004). 9 Value used for rapid degradability, in the GasSim model verification (Attenborough et al., 2002); 10 Estimated from Jensen and Pipatti (2003). 11 Considering t1/2 = 4-7 yr as characteristic values for most developing countries in a tropical climate. High moisture conditions and higly degradable waste. *Adapted from: Chapter 3 in GPG-LULUCF (IPCC, 2003). MAT Mean annual temperature; MAP Mean annual precipitation; PET Potential evapotranspiration. MAP/PET is the ratio of MAP to PET. The average annual MAT, MAP and PET during the time series should be selected to estimate emissions and indicated by the nearest representative meteorological station IPCC Guidelines for National Greenhouse Gas Inventories 3.17